1. Field of the Invention
The present invention relates to fiber optic networks and methods of transmitting and receiving data along fiber optic networks.
2. Background of the Prior Art and Related Information
Fiber optic distribution networks are becoming increasingly important for the provision of high bandwidth data links to commercial and residential locations. Such systems employ optical data transmitters and receivers (or xe2x80x9ctransceiversxe2x80x9d) throughout the fiber optic distribution network. Such transceivers convert electrical signals to optical signals for optical transmission over optical fibers and receive optical signals from the fibers and convert the modulated light to electrical signals. In an Active Optical Network (AON) such transceivers are employed to provide optical-to-electrical-to-optical conversion at each node in the network. To enable high bandwidth data transmission, these transceivers must incorporate high speed electrical circuits along with active and passive optical components, which results in each transceiver being a relatively high cost component. The need for large numbers of transceivers in an AON fiber optic network thus adds considerable cost to the fiber optic network.
The Passive Optical Network (PON) architecture was designed to eliminate the need for optical to electrical conversion, and hence transceivers, at each node of the fiber optic network. The PON architecture employs passive optical components such as beam splitters and filters at the network nodes instead of active optical components. The PON architecture thus has significant cost benefits relative to AON fiber optic networks. The PON architecture was also designed for two way, point to multipoint data communication. Therefore, the PON architecture has significant potential for xe2x80x9clast milexe2x80x9d applications where both two way data transfer and point to multipoint broadcast to end users are desired. Nonetheless, the full potential of PON optical fiber networks has not been achieved in such applications due to problems in providing an effective combination of point to multipoint full duplex digital transmission at high data rates and analog broadcast transmission. Combining these involves both continuous and burst mode transmitters and receivers, precise optical packaging, and effective analog and digital signal separation and amplification.
More specifically, a typical data burst or packet comprises a relatively short, high density burst of data. Each burst is typically followed by a relatively long period during which the transmitter is asleep, before the next data burst. During this sleep period another transmitter may be active on the same fiber. Such burst transmission may thus allow multiple transceivers to share an optical fiber on a time division multiple access (TDMA) basis. Also, such burst transmission may allow one receiver to be coupled to receive data from many transmitters on a time multiplexed basis, whether by sharing of a fiber or with separate fibers. Burst transmission is employed in PON fiber optic data distribution networks which couple a central data distribution transceiver to multiple end user transceivers on a TDMA basis. Also, continuous and burst transmission need to be combined in a PON fiber optic data distribution network providing broadcast transmission. For example, a central data distribution transceiver would transmit in a continuous mode, whereas the end user transceivers transmit in a burst mode back to the central data distribution transceiver. Both burst mode transmission and continuous mode transmission can create difficult constraints on transmitter performance, especially at high data rates. Providing full duplex transmission also requires Wavelength Division Multiplexing (WDM) with two wavelengths of light. Adding broadcast analog, such as Cable TV (CATV), would require a third wavelength of light. WDM in turn requires that the different wavelengths of light can be accurately separated as needed at the network nodes. The difficulty increases with the number of separate wavelengths being discriminated. Large networks with many nodes require precise, compact and cost effective configurations of such optical components. These constraints are difficult to meet simultaneously. Finally, signal to noise problems are exacerbated in analog broadcast and recovery over PON networks. A PON split of 32 adds about 17 dB loss of optical signal. User distance ranges from the central station of the order of 20 km will add an additional 8 dB loss. This can result in problems meeting minimum signal to noise (S/N) ratios with conventional signal separation and amplification circuitry.
From the above it will be appreciated that providing a combination of high data rate full duplex and point to multipoint broadcast transmission, and analog broadcast capability, in a PON architecture presents extremely difficult problems. Also, it is extremely important to provide solutions to these problems without significantly increasing the costs of the system.
The present invention provides a passive optical network (PON) which superimposes distribution of analog signals (AM modulation) like CATV and DBS signals over PON architecture.
In a first aspect the present invention provides a passive optical network, comprising a central station including a first optical transceiver for transmitting analog and digital signals along an optical fiber at first and second wavelengths of light, respectively, and for receiving digital optical signals in burst mode from said fiber at a third wavelength of light. The passive optical network further comprises an optical networking unit coupled to an optical fiber of the network, the optical networking unit including a second optical transceiver for transmitting digital optical signals to said central station in burst mode at the third wavelength of light and optical means for resolving the analog and digital signals from the central station, said optical means comprising optical components mounted via a radiation curable adhesive on a substrate at least a portion of which is transparent to the radiation. The passive optical network further comprises a passive optical network node, coupled to plural optical fibers of the network and configured between said central station and said optical networking unit, for directing said wavelengths of light between said central station and said optical networking unit.
In a preferred embodiment of the passive optical network, the first wavelength of light is about 1520-1600 nm. and the second wavelength of light is about 1440-1500 nm. Alternatively, the first wavelength of light may be about 1580 nm. and the second wavelength of light about 1480-1550 nm. The third wavelength of light may be about 1280-1380 nm. The analog signal preferably comprises an amplitude modulated RF signal. For example, the analog signal may comprise a cable TV signal. The analog signal may also comprise a DBS signal. The digital signals in turn may comprise data packets. For example, the digital signals may comprise internet data.
Accordingly, it will be appreciated that the present invention provides a passive optical network which is capable of point to multipoint full duplex digital transmission at high data rates and which also provides analog broadcast transmission. Further aspects of the present invention, and further features and advantages of the present invention, will be appreciated from a review of the following detailed description of the invention.